Drivers of Dyadic Cofeeding Tolerance in Pan: A Composite Measure Approach

SIMPLE SUMMARY: In this study on zoo-housed chimpanzees and bonobos, we propose a novel operational measure to quantify how tolerantly animals cofeed around a food source. Using an experimental set-up, we measured five behavioral variables that reflect positive and negative aspects of cofeeding behavior. Using a dimension reduction analysis technique, we found a two-dimensional tolerance model that we labeled “Tolerant Cofeeding” and “Agonistic Cofeeding”. In both species, scores on these two dimensions were predicted by sex, relatedness and social bonds in a similar fashion. High-value relationships between individuals that consist in mutual affiliation and support during aggressive interactions resulted in higher tolerance around food sources, while highly competitive dyads that show more mutual aggression showed lower tolerance. Bonobos and chimpanzees did not differ in their overall cofeeding tolerance, which likely reflects their adaptability to fluctuating social and ecological circumstances. This methodology can now be applied to other animal species to further investigate how variation in social and ecological environments influences the tolerance levels of social bonds, both at the dyadic and group level. ABSTRACT: This study aimed to construct a composite model of Dyadic Cofeeding Tolerance (DCT) in zoo-housed bonobos and chimpanzees using a validated experimental cofeeding paradigm and to investigate whether components resulting from this model differ between the two species or vary with factors such as sex, age, kinship and social bond strength. Using dimension reduction analysis on five behavioral variables from the experimental paradigm (proximity, aggression, food transfers, negative food behavior, participation), we found a two-factor model: “Tolerant Cofeeding” and “Agonistic Cofeeding”. To investigate the role of social bond quality on DCT components alongside species effects, we constructed and validated a novel relationship quality model for bonobos and chimpanzees combined, resulting in two factors: Relationship Value and Incompatibility. Interestingly, bonobos and chimpanzees did not differ in DCT scores, and sex and kinship effects were identical in both species but biased by avoidance of the resource zone by male–male dyads in bonobos. Social bonds impacted DCT similarly in both species, as dyads with high Relationship Value showed more Tolerant Cofeeding, while dyads with higher Relationship Incompatibility showed more Agonistic Cofeeding. We showed that composite DCT models can be constructed that take into account both negative and positive cofeeding behavior. The resulting DCT scores were predicted by sex, kinship and social bonds in a similar fashion in both Pan species, likely reflecting their adaptability to changing socio-ecological environments. This novel operational measure to quantify cofeeding tolerance can now be applied to a wider range of species in captivity and the wild to see how variation in local socio-ecological circumstances influences fitness interdependence and cofeeding tolerance at the dyadic and group levels. This can ultimately lead to a better understanding of how local environments have shaped the evolution of tolerance in humans and other species.